Visual Design Softscape  AB

A few words on integrating unmanaged code into your Visual Basic .NET or C# application.

If you have C/C++ code you like to include in your project without having to rewrite the code or if you have header files and lib files intended for C/C++, Managed C++ may be what you need. With Managed C++ you can easily write a wrapper class in managed code, which calls out to unmanaged code.

I have provided a small sample here.

The project is called vdSID and the single class it exposes is simply called Lookup. I also provide a small Visual Basic .NET project to demonstrate its usage.

Lookup has the following static methods (in C# syntax):

  • static int LookupUserGroupFromRid( string TargetComputer, int Rid, [out] string Domain, [out] string Name )
    static int LookupAliasFromRid( string TargetComputer, int Rid, [out] string Domain, [out] string Name )
    Use these to retrieve the localized name of a group or alias, respectively. Well-known RIDs can be found in the testSID Visual Basic .NET sample or in the SID.cpp file.
  • static void sample_asmInc( ref int pVal )
    static void sample_asmInc( int *pVal )
    Example methods showing how to use assembly language in your .NET project. The passed parameter will be incremented by one. Of course, there will be a tremendous overhead involved here, so don't expect it to be fast. If you on the other hand would like to, say create a greay-scale image from a color photo, this technique could actually prove quite useful. The second overloaded version of the method can be used when calling from a piece of unsafe C# code and should be quite faster than the first one (but cannot be used from Visual Basic .NET).
  • static void string[] sample_stringSplit( string strToSplit )
    Example method showing how to return an array of managed objects (Strings). Pass in a string and get back an array of strings, one element for each character in the passed string. The same teqchnique will work for your own managed classes as well (just declare them with "__gc" and you're on track).

Sorry for not providing any instance methods - I just ran out of imagination!

Here is a quick-start on how to add some old C code to your .NET project:

  1. Create a C++ .NET Class Library.
  2. Change the class name to something better than Class1 (no, Class2 is not better).
  3. #include <windows.h> in Stdafx.h. This advice is not a performance issue (ten years ago precompiled headers had a huge impact on compile times, but today you won’t even notice the difference). I’ve run into problems by having it placed in other locations. #include <vcclr.h> in your managed class' implementation (.cpp).
  4. Add a generic C++ class. This is your unmanaged class.
  5. Add your C code to the unmanaged class' implementation and write interface declarations for it in the header file (.h).
  6. Write the interface you want to expose to your .NET application in the managed class’ header file. To declare out and reference parameters you need “using namespace System::Runtime::InteropServices;” in order to acquire the [In] and [Out] attributes.
  7. In the managed class’ implementation file, write the code you need to bridge the gap between the managed types and the native C types. Most notably it is strings that differ. Remember that in C++ you need to explicitly work with object pointers. Therefore, a reference to a “String” will become “String**” – not a one but a two level indirection. The casual C++ programmer may easily forget this. In this file you'll also include any header file you need to get the work done (if you're about to write a wrapper of a third-party API, for example).
  8. You can use any .LIB-files needed under project properties, Linker, Input, Additional Dependencies. vdSID uses netapi32.lib.
  9. Now you’re on your own with MSDN as your trustworthy companion.

Happy Programming!

Ekeforshus Ekeforshus AB 2004-09-06